Hydraulic brake booster



more particularly to'a brake booster hydraulic pressures operate the booster.

Patented Jan. 12, 1943 Ni .oFFlcE 7 HYDRAULIC BRAKE BOOSTER Berteli Stelzer, .St. Petersburg, Fla., assignor to William Stelzer,

Application October 10, 1941, Serial No. 41 4,46! Claims. (01. 188-152) This invention relates to brake boosters and tion with a conventional hydraulic braking system where the booster is operated by an expansible motor mechanism and controlled by the of the master cylinder and the wheel cylinders. This invention is related in its use and purpose to a construction disclosed in my Patent No. 2,260,490, issued October 28, 1941. ,The object of the invention is to provide a more simplified construction and this is accomplished by a novel arrangement of the essential booster partsso thatthey can also be used as control elements.

Another object is tominimize the number of parts and thereby reduce the chance for defects.

A. further aim of the invention is to provide a booster cylinder which consists merely of an open tube and is sealed at both ends with conventional seals which are utilized to control the power to Another advantage is to use seals of uniform size and to transmit their actions by means of to oppose each other and to operate the control valve to direct the powerto-the expansible motor mechanism. 'A further purpose of the novel lever properly proportioned levers in coniuncmeans,. described hereinafter, is to provide a minimum movement of the control seals and'a maximum travel of the control valve.

A still further object is. to provide maximum reservoir space for the powermeansand to place all essential parts within for protection.

spectio'n of the drawing, wherein:

The single figure is a cross sectional view' of the booster and expansible motor mechanism with the conventional braking system shown diagrammatically.

- Describing the invention now in detail, there is shown a conventional master cylinder I oper- Other I advantages and aims will become apparent by in- 1 cylinder serves to ated by a brake pedal 2 to produce a hydraulic pressure in the primary line 3 and which ordinarily is in communication with the secondary or high pressure line 4 leading to the'wheel cylinders 5 of which there are usually four but only one is shown in ordernot to encumber the draw ing. Line 6 thereby. indicates the connection to the other wheel cylinders. Between lines 3 and 4 the booster unit is interposed and this merely consists of a hydraulic booster cylinder 1 secured to the housing 8 of the expansible motormech anism. Cylinder 1 merely consists of a tube which is open at both ends and in which slides a piston 9 provided with a seal l0 and slidably engaged by a piston rod II to which is rigidly secured the I and n'.

necting links mechanism around Detroit. Mich.

expansible motormechanism. The diaphragm. 7

i3 is secured to housing 8 with bolts I4 and the cylinder cover 5 which forms the chamber l6 into which fluid pressure is applied when the expansible motor mechanism is operated. The booster unitis shown in the oil position and urged into this position by return springs l1 The booster cylinder at one end has a 'seal l8 and a sliding sleeve I9 through which the piston rod II extends and which engages a lever v20 pivotally anchored at 2| b'yan abutment 22 The other end of the lever secured to housing 8. 20 is provided with a pin 25 and engages con- 24 (of which only'one is shown) connected atthe other end through a lever 26 which is pivotally connected at 21 by means of a pin extending through to piston 28 provided witha seal 29 which is held in place by spring 11. Piston 28 has a slot 30 to connect-lever 26 which engages cylinder 1 at 3|. An extension 32 extending from lever 26 is adapted to operate sleeve 33 which slides into valve housing 34 secured to housingt at 35. A hole 36 in housing 34 is of such size as to serve as a stop for extension 32 to obtain the desired valve travel. The valve has a ball 31 seated on valve seat 38 by the pressure the supply of air from the atmosphere for which an air cleaner 4!! is provided. The valve housing is bored out to provide a chamber 4| to which ads a'fluid passage 42 from chamber I6. A passage 43 serves to provide communication between the atmosphereand chamber 44. 1

The booster cylinder 1- is secured to the housing 8 by means of bolts 45.. A slot 46 in they booster provide clearance for lever 26. The primary line 3 leads through housing 6 to the primary pressure chamber 41, whereby 48 may indicate a grommet fitting or'seal toprevent air from entering into the expansible motor line 3. Line ,4 is connected in a like manner to the secondary chamber 49 and has a'fltting 48'. V

To hold piston 9 in the proper positionwhen the booster mechanism is in the "oiP position I provide a snap ring 50. This ring is so positioned I a passage is opened beto a pin-23 extending of a spring 39 to close ofi 55 in sleeve l9 houses a wick saturated with brake fluid.

The housing 8 of the expansible motor mecharnsm forms a vacuum reservoir chamber 56 which is in communication with the intake manifold or other source of vacuum or power 51 through a vacuum line 58 into which a check valve 59 is interposed.

Having described the construction of the novel braking system I shall now describe its operation. To simplify the description I divide the system into a primary or low pressure circuit and asecondary or high pressure circuit. The primary circuit includes the fluid under line pressure in the master cylinder, the primary line 3, and chamber 41 of the hydraulic brake booster. The secondary circuit includes the fluid in the wheel cylinders 5, the pressure line 4 and chamber 49 of the hydraulic brake booster.

In the off position, as shown on the drawing, the primary circuit and the secondary circuit communicate and therefore have the same hydraulic pressure. The object of the hydraulic booster is to augment the pressure of the primary circuit to produce a secondary or higher pressure level in the secondary circuit which oper ates the wheel cylinders.

Assuming now that the booster and braking system is in the "oii position as shown on the drawing and that the operator depresses brake pedal 2 to apply the brakes, a pressure is produced in the master cylinder l and therefor in.

the primary circuit 3. This pressure is communicated to chamber 41, through passages 54 and 53, past piston rod 52 and through passage 5| to the secondary circuit which consists of chamber 49, line 4 and wheel cylinders 5. Thus wheel cylinders 5 apply thebrake shoes to the brake drum. Since the effort to expand the brake shoes before they contact the drum is small, the fluid pressure is not sufllcient to engage the valves and to apply power as spring l'l' has sufficient stiffness to oppose sleeve ill on which the primary pressure acts. As the brake shoes come in contact with the brake drum and the operator continues to depress the brake pedal the resistance, and consequently the hydraulic pressure, increases, whereby sleeve l9 and seal l8 overcome spring I? and move lever 20 which is pivotally anchored. Lever 20 through links 24 moves lever 26 which is pivoted at 3|, thereby moving piston'28 to decrease the volume of chamber 49. The movement of piston 28 is a fraction of the movement of sleeve I9 so that when the pressure in chamber 41 and 49 is the same, the sleeve l9 has no difliculty to overpower piston 28. As lever 26 moves about point 3! extension 32 advances sleeve 33 towards ball 31 until it comes in contact with it whereby communication between the source of power or, supply of vacuum from manifold 51 and chamber 56 is shut off from line 42 and chamber 16 of the expansible motor mechanism. At this stage a new resistance is introduced in the form of spring 39 so that the pressure of the primary circuit must be increased substantially before power is applied. This spring 39 has the additional purpose to provide the desired calibration for the point of application of the power whereby spring I1 is merely of sufficient strength to return the piston I2 and diaphragm l3 or the expansible motor mechanism into the "oil" position. Thus the stifl'ness of spring 39 in addition to spring l1 determines the point where power is applied. When thebrake shoes are well in contact with the brake drum and the effort to operate the mas ter cylinder has reached a point where the help of the booster becomes desirable, spring 39 yields and permits further movement of levers 29 and 26, unseating ball 31 from valve seat 38, admitting air pressure from the atmosphere through air cleaner 40, passage 43 and chamber 44 into cham. ber 4|, line 42, and chamber I5 of the expansible motor mechanism. The air admitted to chamber 16 moves diaphragm piston l2 and with it piston rod I I until the latter seats on piston 9, shutting on communication between chamber 41 and chamber 49 by closing passage 5|. Thus the operation of the control valve 31 by the pressure of the primary circuit depends on the resistance of springs ll, 39 and 11 whereby the latter helps to open the valve to admit power and springs 39 and l'l-urge said valve to close and thereby to shut oif the supply of power to the. expansible motor mechanism. After piston rod II has seated itself on the booster piston 9, the piston 9, piston rod H, and diaphragm piston l2 move in unison to reduce the volume of chamber 49, being helped by the primary. pressur in chamber 41, which acts on piston 9, whereby the hydraulic pressure in the secondary circuit is increased and is greater than the pressure in the primary circuit. The pressure in the secondary circuit is the sum of the pressure in the primary circuit and the additional pressure produced by the action of the expansibl motor mechanism.

The. arrangement of the control elements is such that the boosted hydraulic pressure in the secondary circuit is a predetermined multiple of the pressure in the primary circuit. Thus, when the boosted pressure has reached the pre-determined multiple of the primary pressure. the control valve is automatically closed, and if the boosted pressure is greater than the predetermined multiple of the primary pressure, the supply of power to the expansible motor mechanism is not only shut oil, but power is released to decrease the help of the expansible motor mechanism until the desired pressure is reached. Assuming now that the pressure in the secondary circuit has reached the predetermined multiple of the primary circuit while the operator maintains the primary pressure by pressing on the brake pedal, the action of sleeve l9 counterbalances the action of piston 28. Due to the lever ratios oflever 20 and 26 a smaller pressure is required on sleeve l 9 to oppose the pressure on piston 28 whereby the ratio and length of levers 20 and 26 are so proportioned that their overall ratio is approximately equal to the booster ratio (whereby I- neglect the difference due to friction and the action 01' the various springs which at higher operating pressures is negligible). As sleeve I9 and piston 28 are balanced their position is indifferent so that a small force is able to move the levers in either direction. Therefore ball 31 is forced to seat on valve seat 38 by the pressure of the coil spring 39 whereby the supply of air pressure to the expansible motor mechanism is shut oflf. This might be called the "holding position where the brake shoes are applied, but the brake pedal is not depressed further.

Assuming that too much power has been admitted to the expansible motor mechanism, 1. e., to chamber l6, then the boosted pressure in chamber 49 is greater than the predetermined multiple which is depending on the booster ratio and, consequently, piston 28 moves to increase chamber 49 and overpowers sleeve l9 through the transmission of the levers 26 and 20. consequently, extension 32 pivoting about point 3| tween chamber l6 and .9 is stopped by stop ring 50 so.

. on the drawing.

by making the seals 29,

to seat and to separate open up a passage bechamber 56. Thereby air pressure is permitted to escape from chamber l6 through passage 42 and through sleeve 33 into reservoir chamber56 so that the'pressure of the piston l2 acting on piston 9 is reduced; consequently the secondary pressure in chamber 49 is reduced. As soon as it is reduced sufliciently moves to permit ball 31 sleeve 33 from ball 31 to where it is overcome again by primary pressure acting on sleeve 1'9, sleeve 33 is moved again to seat on ball 31 so that the booster is in the holding position."

When the operator releases the foot pressure 7 on the brake der 1, is reducedthereby the pressure on sleeve I9, is relieved so that spring 11, spring 39, as well as the fluid pressure in chamber 49 act jointly to turn lever 26 about pivot 3| whereby extension 32 moves sleeve 33 away from ball 31, opening the passage so that the air under pressure in chamber l6 may escape through passage 42, chamber 4!, and sleeve 33 into reservoir chamber 56, to be evacuated from there through vacuum line- 58 and intakemanifold 51. As the air from chamber I6 escapes spring H in unison with spring I! pushes the diaphragm piston l2 into the oiT" position, Before the diaphragm piston I2 has reached the oil position, 'piston that when the diaphragm piston 2 is moved further to its off" position a fluid passage isopened through passages 54, 53 and to establish communication betweenthe primary circuit circuit. Therefore fluid from chamber 49 is forced through passage 5| to return to themaster cylinder I until the brakes'hoes are urged into their released position by the brake shoe return springs which are standard elements of conventional brakes and are therefore not shown The braking system is now position as illustrated on the pedal the pressure in master cylinagain in the "01? drawing.

To simplify thedescription of-the booster I have called piston 28 a control piston 'butit is apparent that this part, as well'as sleeve l9 and seal is are essential parts of the booster cylinder because a hydraulic cylinder in its essential parts consists of a cylinder, a piston, a piston rod, as well as convenient parts such as a cylinder head and stuifing box to close oil the ends to complete the cylinder chambers. trol piston 28 may be head which I am using to measure the boosted pressure. Seal l8 and sleeve l9 may be considered as a stufiing box which is used in the novel construction to measure the primary pressure. A great simplification of construction is obtained I0 and I8 of the same diameter.- It is a particular advantage of the transmitting control levers 26 and that their effective ratios maybe changed without any radical alteration of the construction. It is particularly easy to change the position of the point of contact 3| to a small extent by removal of the metal from cylinder 1.

It is apparent that the novel booster in its principle can be constructed in many ways different from that shown, therefore, I do not wish to limit the scope of the ticular embodiment shown by way of illustration, or otherwise than by the terms of the appended claims.

I claim:

and the secondary invention to the par-.

and consequently in the primary circuit,

control piston in said 7 said wheel cylinders,

.1. In a braking system for automotive vehicles having a hydraulic master cylinder operated by the operator and wheel cylinders to'apply the brake shoes, in combination, a hydraulic brake booster consisting of a cylinder, a booster piston therein to divide said cylinder into a primary or low pressure chamber, and a secondary 'or high pressure chamber, fluid pressure transmitting means from said primary pressure chamber, fluid pressure transmitting means from said secondary pressure chamber to said wheel cylinders, an'expansible mechanism to operate said boosterpiston. a source. of power to operate said expansible motor mechanism, valve means to direct power to and from said expansible motor mechanism, a primary pressure chamber responsive to the hydraulic pressure produced by said master'cylinder, a control piston in said secondary pressure chamber responsive to the boosted hydraulicpressure, mechanical lever means to transmit the force'produced by one control piston to oppose the other, said lever means being so proportioned that the forces of the control pistons are balanced when the desired booster ratio is obtained, said valve means'being responsive to the excursions of said lever means whereby an excursion due to the yielding of the control piston in said secondary pressure chamber to the control piston in said primary pressure chamber urges said valve to direct power from said source of power to said expansible motor mechanism to increase the hydraulic pressure in and where an' excursion due to yielding of the piston in said primary pressure chambertothe control piston in said secondary pressure chamber urges said valve means to decrease the power directed to said expansible motor mechanism, and means to provide passage of hydraulic fluid from said secondary chamber to said primary chamber when said booster is in the oil position and the brake pedal released. 2. In a braking system for automotive vehicles having a hydraulic master cylinder onerated by the operator and wheel cylinders toapply the brakes, in combination, a hydraulic booster cylinder, a booster piston in said booster cylinder dividing said booster cylinder into a primary pressure chamber and a secondary pressure pressure transmitting means from said secondary pressure chamber to said wheel cylinders, an expansible motor mechanism to operate said booster piston, a source of responsive to the excursions of aid lever means to operate said valve means.

- 3. In a hydraulic braking system for automotive vehicles having a hydraulic master cylinder operator, wheel cylinders to apply the brake shoes, and fluid pressure transmitting means from said master to said wheel cylinders, in combination, a hydraulic booster interposed in said fluid pressure transmitting means which dimaster cylinder to said vides said braking system into a primary circuit whose pressure is produced by said master cylinder, and a secondary circuit whose pressure is boosted by said hydraulic booster and is in communication with said wheel cylinders, an expansible motor mechanism to operate said hydraulic booster, a source of power to operate said expansible motor mechanism, valve means to direct power to and from said expansible motor mechanism, balancing lever means responsive to the pressure of said primary circuit and said secondary circuit to weight said pressures and to operate said valve means to direct more power to said expansible motor mechanism when the secondar pressure is' too low. and to reduce the power admitted to said expansible motor mechanism when the pressure of said secondary circuit is too high, means to provide passage of fluid from said secondary circuit to said primary circuit when the booster is in the off position, said booster, said expansible motor mechanism, said valve means and said lever means forming a single, self-contained unit. 4. In a hydraulic braking system for automotive vehicles having a master cylinder operated by the operator, wheel cylinders to apply the brake shoes and a fluid pressure transmitting line from said master cylinder to said wheel cylinders, in combination, a hydraulic booster interposed into said fluid pressure transmitting line dividing said hydraulic braking system into a primary circuit whose pressure is produced by said master cylinder and a secondary circuit in communication with said wheel cylinders, an expansible motor mechanism to operate said hydraulic booster, a source of power to operate said expansible motor mechanism, valve means to direct power to and from said expansible'motor mechanism, said'hydraulic booster consisting of acylinder and a booster piston therein said piston dividing said cylinder into a primary circuit chamber and a secondary circuit chamber, a piston rod operated by said expansible motor mechanism to move said booster piston, a slidable steal between said piston rod and said cylinder to seal the primary circuit chamber, a seal slidable in said cylinder to seal said secondary circuit chamber, mechanical,

lever means responsive to the hydraulic pressure of the primary circuit acting on said seal that seals said primary circuit chamber urging said valve means to increase the power directed to said expansible motor mechanism, mechanical lever means responsive to the hydraulic pressure of the secondary circuit acting on said seal that seals said secondary circuit chamber urging said valve means to decrease the power directed to said expansible motor mechanism, and means to provide a hydraulic passage between the primary and the secondary circuit when said booster is in the "0115 position.

5. In a hydraulic braking system for tivefvehicles'havin'g a master cylinder operated by the operator and wheel cylinders to apply the brake shoes; in combination, a hydraulic brake booster cylinder, a booster piston slidable in said hydraulic brake booster cylinder and acted upon by the hydraulic pressure produced by said master cylinder, an expansible motor mechanism to operate said piston to produce a higher pressure level for the operation of said wheel cylinders, fluid pressure transmitting means between said master cylinder and the low pressure side of said hydraulic brake booster cylinder, fluid pressure transmitting means between said wheel cylinders and the high pressure side of said hydraulic brake booster cylinder, a source of power to operate said expansible motor mechanism, a valve to direct power to and from said expansible motor mechanism, mechanical lever means responsive to the hydraulic pressure produced by said master cylinder to urge said valve to increase the power directed to said expansible motor mechanism, and mechanical lever means responsive to the hydraulic pressure in said wheel cylinders to urge said valve to decrease the power directed to said expansible motor mechanism, said lever means having a ratio giving the master cylinder pressure the advantage so that the opposing forces urging the operation of said valve are counteracted and balanced when the boosted hydraulic pressure in said wheel cylinders has reached the desired and pre-determined multiple of the hydraulic pressure produced by said master cylinder.

BERTELI STELZE R.

automo- 

